Carrier transmission over power circuits



June 2. 19.25-

R. K. HONAMAN CARRIER TRANSMISSION OVER POWER CIRCUITS Filed April 29,1924 INVENTOR IRK. HmmY/nan/ ATTORNEY Patented June 2, 1925.

UNITED STATI-:s

PATENT OFFICE..

RICHARD IK, HONAMAN, OF BLOOMFlELD, NEW JERSEY, ASSIGNGR T AMERICANTELEPHONE & TELEGRAPH COMPANY, A CORPORATION OF YQRK.

CARRIER TRANSMISSION OVER POWER. CIRCUITS.

Application led April 29, 1924. Serial N'o. 709,898.

To all whom may concern: p

Be it known that I, RICHARD K. HoNA- MAN, residing at Bloomfield, in thecounty of Essex and State of New Jersey, have invented certainImprovements in Carrier Transmission Over Power Circuits, of which thefollowing is a specification.

This invention relates to the use of power circuits for the transmissionof signaling currents, and lmore particularly to arrangements wherebycarrier transmission channels may be related to the conductors of apower system.

In accordance with the present invention, advantage is taken of the factthat .the current transformers, which are ordinarily associated with apower system in order to step down the current actually transmitted to avalue suitable for use with nary current measuring instruments, e suchcharacteristics that, although normilly designed for the transmission yof power frequencies, they will eiiciently transmit the much higherfrequencies employed in carrier transmission. The carrier apparatus isconnected to the circuit `which includes the current measuring or othertranslating device which is normally inductively connected to the powercircuit, and in order to prevent an substantial increase in theimpedance o the instrument i the connection is made through a ing a verylow impedance at the pew e. frequency and a considerably higher'impedance at the carrier current frequencies, v

rthe invention will now be more fully understood from the followingdescription when read in connection with the accomvif; psig: irawings,Figures 1 and 2 of which illustrate two different arrangements embodyingthe principles of the invention.

Referring to Fig. 1, G designates a power generator of the well knownpolyphase type 1, 2 and .3, respectively, of the power dishaving itsstarwindings connected to the tribution system. The transformers 11, 12and 13 are transformers which step down the current flowing through themeasuring instruments to values appropriate for indication by themeasuring instruments. The terminals of the three measuring instrumentsare normally connected together (as indicated by the dotted lineconnection in the figure) and grounded througha conductor ofsubstantially no resistance as shown.

In practice, the current transformers such as 11, 12 and 13 have theirwindings constructed with relatively few turns so that thedistributedcapacity' is very small, and although these transformers are primarilydesigned for the transmission of power frequencies such as currentsinthe neighborhood of cycles, they are quite eicient transformers at themuch higher frequencies employed in carrier transmission. Consequentlyin superposinga carrier channel on a power distribution system it addsgreatly to the economy of the system to be able to utilize the currenttransformers for associating the carrier channel with the powerconductors. In order to accomplish this result, the present inventioncontemplates opening the normal connection between two of the instrumentcircuits,vfor example, 1 'i and 2', and connecting the terminals of thecarrier channel C to the two instrument terminals as indicated.

In order that this may be` done without disturbing the measuringapparatus, the impedance looking into the carrier channel must be madevery low forv the power frequencies. The carrier channel may be made tohave a very low impedance to the power frequencies if the high-passfilter F which is included in the channel to suppress power frequenciesand the lower harmonics thereof, is properly designed. The impedancelooking into the filter isv not greatly different from the impedance ofthe Erst section of the filter. Consequently if the filter is given ashunt termination, as illustrated, its impedance will be very low, forthe shunt inductance element of the first section of the filter may bereadily designed to offer a very low impedance to 60 cycle currentswithout changing the action of the lilter in its range of freetransmission. The power currents to be measured will therefore passthrough the measuring, instrushunt these instruments by means of condensers, as indicated, to by-pass the carrier frequencies.

A modified arrangement is illustrated in Fig. 2 which differs from thatof Fig. 1 in that one terminal of the carrier channel is connected toground and the other terminal is connected to a conductor common to thethree measuring circuits so that the carrier current will be transmittedover the three wires of the distribution system in parallel.

Normally the current measuring instruments will have their terminalsjoined together and the common terminal connected to ground, preferablythrough an additional measuring instrument 24, which measures'the totalcurrent flowing in all three conductors of the distribution system. Thecarrier channel C may be connected to the circuit of the currenttransformers by opening the normal ground connection shown in dottedlines in Fig. 2 and connecting the terminals of the carrier channel intothe circuit at the point where it is o ened up. As in the case of Fig.1, it is un esirable that any substantial impedance be introduced in themeasuring circuit at the power frequency, and accordingly the filteris'constructed to have a shunt termination. The terminal shuntinductance element of the filter, as already stated, may then havepractically negligible impedance at the power frequency without changingthe action of the filter at carrier frequencies.

It will be obvious that the general principles herein disclosed may beembodied in many other organizations widely different from thoseillustrated without departing from the spirit and scope of the inventionas defined in the following claims.

What is claimed is:

1. In a system for signaling over power conductors, a power source,power conductors for transmitting power from said source to a load,current transformers associated ing a filter connected in circuit withsaid transformers and having a very low impedance at power frequencies.

2. In a. system for signaling over power conductors,a power source,power conductors fortransmitting power from said source to a load,current transformers associated with said conductors for transformingthe current to be applied to translating devices, carrier apparatus, andmeans to connect said carrier apparatus to said power conductors throughsaid current transformers, comprising a high-pass filter included incircuit with said transformers and having a shunt termination so thatits impedance will be very low at power frequencies.

3. In a system for signaling over power conductors, apower source, powerconduc-` tors for transmitting power from said source to a load, currenttransformers associated with said conductors for transforming thecurrent to be applied to translating devices, carrier apparatus, andmeans to connect said carrier apparatus to said power conductors throughsaid current transformers, comprising a high-pass filter having itsterminals connected in circuit with said current transformers, saidfilter being so designed that its impedance at power frequencies will bevery low.

4. In a system for signaling over power conductors, a power-source,power conductors for transmitting power from said source to a load,current transformers associated with said conductors for transformingthe current to be applied to translating devices, carrier apparatus, andmeans to connect said carrier apparatus to said power conductors throughsaid current transformers, comprising a high-pass filter having itsterminals connected in circuit with said translating devices, saidfilter having a shunt termination so that its impedance to currents ofpower frequency will be very low.

In testimony whereof I have signed my name to this specification this26th day of April, 1924.

